1. Field of the Invention
The present invention relates in general to electrochromic devices, and more particularly, to an electrochromic medium for use in an electrochromic device which comprises one or more controlled diffusion coefficient anodic and/or cathodic materials.
2. Background Art
Electrochromic devices have been known in the art for several years. While the utilization of electrochromic devices, such as electrochromic mirrors, has become increasingly popular, for example, among the automotive industry, issues relating to operating current and cell spacing of an electrochromic device remain problematic for a plurality of applications.
It is well known that the operating current of an electrochromic device is proportional to the diffusion coefficients of the electrochromic materials in the device and inversely proportional to the distance between the inner surfaces of the two spaced-apart substrates (Electrokhimya 21 (7) 918-22, 1985). Previous attempts to influence the operating current of an electrochromic device have relied on changing the solvent of the electrochromic medium (U.S. Pat. No. 5,140,455) or incorporating additives into the electrochromic medium (U.S. Pat. No. 5,142,407). The present disclosure describes the intentional modification of the electrochromic materials themselves to manipulate their diffusion coefficients, thereby controllably altering the operating current and/or cell spacing of an associated electrochromic device. This approach permits the use of a most preferred solvent rather than a more toxic or expensive alternative, while avoiding the additional cost and process complications of incorporating an additive. It will also be understood that, by using electrochromic materials with reduced diffusion coefficients, among other things: (1) operating current and/or cell spacing can be decreased to reduce the volume and cost of the electrochromic medium; (2) design parameters such as device coloring/bleaching time can be controllably altered; (3) manufacturing efficiency can be materially increased as a result of decreased device cell spacing; and (4) the formation of color bands (i.e. segregation) can be reduced or eliminatedxe2x80x94just to name a few.
It is therefore an object of the present invention to provide an electrochromic medium which comprises one or more controlled diffusion coefficient anodic and/or cathodic electrochromic materials which remedy the aforementioned detriments and/or complications associated with the use of conventional electrochromic devices and associated medium components.
These and other objectives of the present invention will become apparent in light of the present specification, claims, and drawings.
The present invention is directed to an electrochromic medium for use in an electrochromic device comprising: (a) at least one solvent; (b) an anodic electroactive material; (c) a cathodic electroactive material; (d) wherein at least one of the anodic and cathodic electroactive materials is electrochromic; (e) wherein the anodic electroactive material comprises a diffusion coefficient less than approximately 8.00xc3x9710xe2x88x926 centimeters squared per second (cm2/s) in propylene carbonate at approximately 25 degrees centigrade and/or the cathodic electroactive material comprises a diffusion coefficient less than approximately 3.00xc3x9710xe2x88x926 cm2/s in propylene carbonate at approximately 25 degrees centigrade; and (f) wherein the anodic and/or cathodic electroactive material comprises a diffusion coefficient controlling moiety which is non-redox active during normal operation of an associated electrochromic device.
The present invention is further directed to an electrochromic medium for use in an electrochromic device comprising: (a) at least one solvent; (b) an anodic electroactive material; (c) a cathodic electroactive material; (d) wherein at least one of the anodic and cathodic electroactive materials is electrochromic; and (e) wherein the anodic and/or cathodic electroactive materials are represented by at least one of the formulae A1-A15 and C1-C5, respectively, as provided herein.
In another aspect of the invention an electrochromic medium for use in an electrochromic device is disclosed as comprising: (a) at least one solvent; (b) an anodic electroactive material; (c) a cathodic electroactive material; (d) wherein at least one of the anodic and cathodic electroactive materials is electrochromic; and (e) wherein the anodic and/or cathodic electroactive material includes: (1) a first moiety; and (2) a diffusion coefficient controlling moiety, wherein the diffusion coefficient controlling moiety comprises at least one constituent which serves to decrease the diffusion coefficient of the first moiety in the at least one solvent relative to the first moiety without the diffusion coefficient controlling moiety.
The present invention is also directed to, among other things, novel anodic and cathodic materials having controllably reduced diffusion coefficients.